Centrifugal blower

ABSTRACT

Centrifugal blower produces a substantially radial discharge and operates efficiently without a scroll.

0 United States Patent 1191 1111 3,859,009

Ballentine 1 Jan. 7, 1975 [5 1 CENTRIFUGAL BLOWER 1,877,347 9/1932 McMurdie .1 416/183 [76] Inventor: Earle W. Ballentine, 127 Lomita FOREIGN PATENTS OR APPLICATIONS -1 El Segundo/C9111 90010 1,046,247 12/1958 Germany 410/1113 1,935,013 1/1971 Germany 4 1 416/186 [22] 1973 723.706 2/1955 Great Britain. 416/186 [21] Appl. No.: 412,564 814,564 6/1959 Great Britain... .1416/188 52,538 5/1942 Netherlands 416/186 152] US. Cl. 416/186 H 511 1111. c1. F04d 29/28 Emmme Everette [58} F1e1d of Search ..416/184,186,182,185 ABSTRACT [56] References Cited Centrifugal blower produces a substantially radial dis- UNITED STATES PATENTS charge and operates efficiently without a scroll.

1,246,090 11/1917 Hagen 416/186 5 Claims, 3 Drawing Figures PATENTED JAN 7 I975 SHEET 10F 2 mm; zm x PATENTEUJAH mi- SHEEI 2 0F 2 CENTRIFUGAL BLOWER BACKGROUND OF THE INVENTION The prior art centrifugal blowers with twelve backward blades which have outlet angles of inclination in the range of 37 to 50 and inlet angles of or more, have high efficiencies when used in a scroll which transforms the high velocity heads produced into static pressure by means of the free vortex developed within the scroll. The entrance blade angle is most efficient when the angle of attack is in the range of 12 to 16. If the angle of attack exceeds 16, severe flow separation occurs at the trailing edge and subsequently over most of the blade upper surface. The effect is to increase the drag produced by the turbulence.

The highest efficiencies are obtained with curved inlet shrouds combined with airfoil shaped blades. The scroll also uses a curved or conical inlet. The prior art empirical equations are well established, with the result that design modifications are easy to calculate. The cost of manufacture is, of course, relatively high. The scroll outlet velocity has a non-uniform magnitude and direction which results in non-uniform heat transfer and temperatures when used with heat exchangers.

Many of the disadvantages of the backward curve blade blower with a 12 blade impeller operating within a scroll are obviated by the new concept blower presented in this invention.

My centrifugal blower consists of an impeller without a scroll. The impeller consists of 16 or more blades which are supported by a backplate at one end and a conical shroud at the other end. The blade inlet and outlet angles of inclination are 28 and 32, respectively. The blade shape is a circular arc, which joints the inlet and outlet velocity vectors with the tangent angles of 28 and 32, respectively. The inlet diameter of the blade is 79.2 percent of the outlet diameter. The prior art blade diameter ratios are 70-73 percent. The inlet and outlet radial velocities are equal and equal to 25 percent of the outlet peripheral velocity. When the radial velocities are equal, the blade inlet width (b,) times the diameter of the blade at the inlet (d will be equal to the blade outlet width (12 times the diameter of the blade at the outlet (d Thus, bg/b equals ai /d and this ratio will equal .792.

The static pressure produced by a backward curved impeller is given by the following empirical equation:

wherein D air density g acceleration of gravity U outlet peripheral velocity 4), blade outlet angle 2 number of blades, and

Ps static pressure in lbs/ft There are two important losses which are inherent in the impeller. The largest loss appears in the impeller eye. The air usually enters the impeller eye through an inlet ring which facilitates the flow of air into the blower wheel and then turns through a right angle prior to entering the blade passages. The impeller eye loss is given by the following expression:

A P, K. 11/2 No where V0 n the air velocity in the impeller eye thus V0 4Q/rrd 2 where Q the air flow rate d, the inlet diameter The other important loss occurs in the blade passages due to flow separation since the relative velocity of the air decreases.

where K 0.2 0.3 and W, relative velocity of air entering the impeller blade passage and W relative velocity leaving the impeller If the inlet and outlet blade angles were equal to each other and also equal to 30, the relative inlet and outlet blade passage velocities would also be equal and cancel each other. The blade angles which I use, namely 28 and 32, result in blade passage losses which are negligible.

The unique combination of design parameters which I have discovered which produce the highest possible efficiency for an impeller operating without a scroll are in the order of their importance as follows:

A. The use of i6 blades instead of 12 blades in a backward curved blade blower.

B. The selection of a blade inlet to blade outlet diameter ratio of 0.792 instead of 0.70 0.73.

C. The combination of conditions A and B with inlet and outlet blade angles of 28 and 32, respectively.

The basic problem in applying the empirical relations is due to the fact that the parameters are not independent. For example, if the inlet diameter is increased, the impeller eye loss will decrease in accordance with the fourth power of the inlet diameter. However, the vortex head will decrease with the square of the inlet diameter. The static pressure increases rapidly with the difference between the inlet andoutlet blade angles but the blade passage relative velocities produce substantial losses which vary with the square of the velocity diffusers.

I believe that my step-by-step analysis has produced a unique parametric combination which will provide the maximum performance obtainable for a blower impeller which operates without a scroll.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustration of the velocity vector distribution of a rotating blade formed in accordance with the present invention;

FIG. 2 is an elevation of an impeller employing the present invention; and

FIG. 3 is a section of the device illustrated in FIG. 2, as seen along a line 3--3 therein.

DETAILED DESCRIPTION FIG. 1 shows the velocity vector triangles based on the analysis which I have presented. When a radially flow impeller is discharging air without any obstruction, the air flow has a maximum value and the direc tion of flow approaches the direction of the vector v, as shown in FIG. 1, which illustrates the vector velocity of air leaving a blade under unobstructed flow. However, if the external air circuit requires a substantial pressure drop, there is a substantial reduction in the velocity v The direction of flow moves towards the radial flow vector v which is the radial vector velocity of air leaving the blade, as seen in FIG. 1. With maximum efficient blower pressure, the direction of flow is substantially radial, i.e., v The calculated performance is about l,080 CFM against a static pressure of about 1% inches w.c. with a 12 inch diameter impeller operating at a speed of 1,750 rpm.

FIG. 2 shows a side view of the blower impeller. The inlet ring which can be either conical or curvilinear is not shown. The curvilinear form is the most efficient. The blades 1 are supported at one end by the backplate 2 and are supported at the other end by the conical shroud 3. There are two methods of attaching the blades 1 to the backplate 2 and the conical shroud, namely, by tack welding or by riveting. When the blades 1 are attached by riveting, the blades 1 are provided with integral right-angled extensions which are not shown. The diameter of hub 4 and the thickness of backplate 3 should be of such magnitudes that the structure resists rocking or other forms of distortion at the maximum speeds required. The impeller must be statically and dynamically balanced where the two planes of correction are the shroud and the backplate.

The noise produced by a centrifugal impeller arises at the blade inlet. If acoustical absorbing material is attached to the hub 4 in the form of a cylinder of similar diameter, there is a great reduction in the noise emitted.

One of the applications of my blower is for circulating air in commercial and industrial ovens. Another important application is for producing air flow through heat exchangers. The blower can discharge into a plenum chamber with low velocity head losses and produce a uniform air velocity through a heat exchanger .the invention in considerable detail for the purpose of illustration, it should be understood that the invention is not restricted to the specific details which I have shown.

It will be apparent to those skilled in this art that many other embodiments, various changes and modifications may be made without exceeding the scope of the invention as defined by the following claims, wherefore, what I claim as my invention is:

l. A centrifugal blower without a scroll comprising:

blade means consisting of 16 identical backward curved blades with inlet and outlet angles of inclination of 28 and 32, respectively, and wherein the ratio of the blade inlet and outlet diameters is 0.792.

2. A radial flow impeller having more than 1 single thickness backward curved blades wherein the angle subtended by the blade is equal to 360 divided by the number of blades and wherein the blade inlet angle is less than 30 and the blade outlet angle is more than 30.

3. The radial flow impeller in accordance with claim 2 in which the ratio of the blade inlet diameter to the blade outlet diameter is at least .75.

4. A radial flow impeller in accordance with claim 2 in which the blade inlet angle is approximately 28 and the blade outlet angle is'approximately 32.

5. A radial flow impeller in accordance with claim 4 wherein the ratio of the blade inlet diameter to the blade outlet diameter is at least .75. 

1. A centrifugal blower without a scroll comprising: blade means consisting of 16 identical backward curved blades with inlet and outlet angles of inclination of 28* and 32*, respectively, and wherein the ratio of the blade inlet and outlet diameters is 0.792.
 2. A radial flow impeller having more than 1 single thickness backward curved blades wherein the angle subtended by the blade is equal to 360* divided by the number of blades and wherein the blade inlet angle is less than 30* and the blade outlet angle is more than 30*.
 3. The radial flow impeller in accordance with claim 2 in which the ratio of the blade inlet diameter to the blade outlet diameter is at least .75.
 4. A radial flow impeller in accordance with claim 2 in which the blade inlet angle is approximately 28* and the blade outlet angle is approximately 32*.
 5. A radial flow impeller in accordance with claim 4 wherein the ratio of the blade inlet diameter to the blade outlet diameter is at least .75. 